EFFICACY OF ABAMECTIN INJECTION AGAINST DERMATOBIA-HOMINIS IN CATTLE

The efficacy of abamectin 1 %, when injected subcutaneously in cattle at a dose of 200 mug/kg body weight, against the larval stages (grubs) of the fly Dermatobia hominis was evaluated in two trials in endemic areas of Brazil and Argentina. Eighteen Holstein x Brahman castrated m ales and 16 Brahman-cross with natural infestations were used. Larvae were counted by instar in situ on both sides of each animal before tre atment, and were expressed, identified as to stage and classified as l ive or dead 10 days after treatment. Further larval counts were made p eriodically until day 79 to evaluate the degree of reinfestation and t he stage of larval development. Reinfestation was first detected in th e abamectin-treated cattle on day 44. Live larvae were found on 6-8 (A rgentina) and on all (Brazil) controls at each post-treatment examinat ion. The difference in numbers of live larvae between treatment groups was statistically significant (P < 0.05) at all post-treatment examin ations. These data show that abamectin at a dose of 200 mug/kg body we ight is highly effective in the treatment and control of established p arasitic stages of D. hominis in cattle. No adverse reactions were obs erved in any of the treated animals.